TUBE AS 6N7551 - Caterpillar

Switches provide information (input) to the main display module. Switches are two state devices. The two states are described below.Closed - The switch connects the control input to the ground.Open - The switch does not connect the control input. The input is floating.Note: See Engine Service Manual, "Electrical System Schematic" for specifications for switches.Fluid Level Switch (Engine Coolant)
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Low Coolant Level Switch (1) Switch (2) Schematic symbol (3) Plastic sleeveThe low coolant level switch is an electronic switch that is activated by the coolant. During normal operation, the low coolant level switch (1) is closed to ground. The switch opens when the level is too low. The operator is notified by the main display module of a very low coolant condition that is in the cooling system.The switch is connected with three contacts. The sensor is supplied with power at connector contact "A" from the main display module. Contact "B" connects to ground. Contact "C" is the switch output. Contact "C" connects to the input of the main display module. See Testing And Adjusting, "CID 111 Engine Coolant Loss" for more information.Note: Do Not remove plastic sleeve (3) from the probe. This plastic sleeve is required for proper switch operation.Pressure Switch (Engine Oil)
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Engine Oil Pressure SwitchThe engine oil pressure switch sends a B- signal to the control board when the oil pressure drops below the trip point of the switch. The B- signal causes the control board to perform an engine shutdown for a low oil pressure fault. The switch is mounted on the outside of an oil gallery of the engine. The exact location depends on the engine model.The switch has normally open contacts and normally closed contacts. Only the normally closed contact "A" and contact "C" are used. Contact "C" connects to the control board. Contact "A" connects to B-.The specifications for the 3E-6455 Pressure Switch are listed below.
Pressure for actuation is 90 21 kPa (13 3 psi).
Pressure for deactuation is 70 21 kPa (10 3 psi).Temperature Switch (Engine Coolant)
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Engine Coolant Temperature SwitchThe engine coolant temperature switch sends a B- signal to the control board when the coolant temperature exceeds the trip point of the switch. This signal causes the control board to perform an engine shutdown for a high water temperature fault. The switch is mounted in the water jacket usually near the front of the engine. The exact location depends on the engine model.The switch has normally open contacts and normally closed contacts. Only the normally open contacts "A" and "B" are used. Contact "A" connects to the control board. Contact "B" connects to the negative battery terminal.